Optical flame detector

ABSTRACT

An optical flame detector having a first photocell focused on a general area and another photocell, connected to electronically oppose the first photocell, more particularly focused on a specific point within the general area. Thus, ambient light-level changes which occur in the entire general area produce voltage generation in both photocells which cancel each other out and, quite properly, do not operate the fire alarm. Yet, the occurrence of flame at the specific point activates the one photocell more than the other and, consequently, does cause operation of the fire alarm.

United States Patent 227 R, 213, 213 D; 250/209, 220 C, 217 F [56]References Cited UNITED STATES PATENTS 2,897,485 7/1959 Johnson 340/228UX 3,303,340 2/ 1967 Hewett 250/220 C Primary Examiner.lohn W. CaldwellAssistant Examiner--William M. Wannisky Attorney-Myron Amer ABSTRACT: Anoptical flame detector having a first photocell focused on a generalarea and another photocell, connected to electronically oppose the firstphotocell, more particularly focused on a specific point within thegeneral area. Thus, ambient light-level changes which occur in theentire general area produce voltage generation in both photocells whichcancel each other out and, quite properly, do not operate the firealarm. Yet, the occurrence of flame at the specific point activates theone photocell more than the other and, consequently, does causeoperation of the tire alarm.

mEmEn M 41372 INVENTOR. BENJAMIN NElGER ATTORNEY OPTICAL FLAME DETECTORThe present invention relates generally to fire alarms, and moreparticularly to improvements for an optical flame detector.

As generally understood, a typical known flame detector includes aphotocell having a specifically assigned area or point of coverage,and'is adapted to trigger an alarm in response to the occurrence offlame at the assigned area or point. This prior art photocellarrangement, however, is vulnerable to sounding false alarms because ofits inability to distinguish between radiation or light-level increaseswhich should not trigger the fire alarm from flaming which should. Forexample, an increase in the ambient light in a warehouse where the flamedetector is installed should not operate the flame detector, butinvariably does since the photocell is geared to react to a light-levelincrease whether it be from flaming or from additional lighting.

Broadly, it is an object to provide an improved flame detectorovercoming the foregoing and other shortcomings of the prior art.Specifically, it is an object to provide a photocelltype flame detectorcapable of distinguishing between ambient light-level changes andflaming at a specific flame-detection point, and of triggering an alarmonly in response to the latter.

An optical flame detector demonstrating objects and advantages of thepresent invention includes two photocells focused by their orientationon an operative area, one of which, however, is further restricted by alens to a specific flame-detection point in the operative area. Thephotocells are electrically connected in opposition such that an ambientlight-level change which, of course, occurs throughout the operativearea effects both equally and results in cancelling voltages. Flaming atthe flame-detection point, however, primarily effects only one photocelland results in voltage generation which is readily put to use to triggera fire alarm.

The above brief description, as well as further objects, features andadvantages of the present invention, will be more fully appreciated byreference to the following detailed description of presently preferred,but nonetheless illustrative embodiments in accordance with the presentinvention, when taken in conjunction with the accompanying drawings,wherein:

FIG. 1 is a simplified circuit diagram of a first embodiment of a flamedetector according to the present invention; and

FIG. 2 is similarly a circuit diagram of a flame detector according tothe present invention, in which a preferred second embodiment thereof isillustrated in detail.

Reference is first made to the simplified embodiment of a flame detectoras illustrated in FIG. 1 and generally designated therein. The essentialstructural features of the detector 10 in this embodiment, as well as inthe embodiment of FIG. 2, consists of a pair of photocells l2 and 14powered by an appropriate power supply 16 which either can bealternating current supplied over power lines or direct current suppliedby batteries. As will be described subsequently herein, the photocellsl2, 14 are operatively arranged to operate an appropriate fire alarm 18,which alarm can consist of an optical signal or a sound signal,whichever is preferred. In other words, the specific nature of the powersupply 16 or of the fire alarm 18 may vary and is not an essential partof the present invention. What is essential is the use of the photocells12, 14 and also the additional aspects of the circuit 10 which will nowbe described in detail and which result in the photocells l2, 14 beingcapable of detecting the occurrence of a flame at a specific point andthereupon causing operation of the fire alarm 18. In this regard, theoccurrence of the flame which, in effect, is an increase in light levelcannot be confused with other occurrences which also increase the lightlevel but which should not result in the operation of the fire alarm 18.Such occurrences, for example, would be an increase in the ambientlighting of a warehouse where the flame detector 10 is installed orperhaps merely an increase in sunlight directed upon the flame-detectionpoint. For commercial utility of the flame detector 10, it is necessarythat it be capableof distinguishing between the foregoing light-levelchanges and that it t be sensitive only to that light-level change whichis the result of the occurrence of flame at a selected flame-detectionpoint.

To the above end, each embodiment of the flame detector 10 hereofincludes the already noted photocells 12, 14, and also an appropriatebridge-type circuit 20 electrically connecting these photocells inopposition to each other such that voltages generated by thesephotocells which are of substantially the same extent cancel each otherout. On the other hand, should there be an overbalance of generatedvoltage, as for example from the photocell 14, this overbalance ofgenerated voltage will flow through the conductor 22 and, in, a wellunderstood manner, be effective in operating the fire alarm 18.

The significance of electrically connecting thephotocells l2 and 14 inopposition to each other as it specifically relates to. the function offlame detection will now be explained. Photocell 12 is physicallyarranged so as to sense and react to any light emanating from aprescribed area 24. Photocell 14, on the other hand, is associated witha light-gathering lens 26 which is optically effective to restrict thepurview of the photocell 14 to a specific point within the prescribedarea 24 which will be understood to be the flame-detection point 28.Specifically, point 28 will be understood to be that point at which theuser of the detector 10 feels is most vulnerable to flame and is thusthe point that this product is designed to sense for the occurrence offlame. This point, for example, may be a specific location on a boileror may be a specific location in a warehouse where highly flammablematerials are stored. In any event, flame detection point 28, as alreadynoted, is specifically sensed for the occurrence of flame by photocelll4 and is within the operative area 24 which is sensed by the photocell12.

With the above understanding, let it be assumed that there is alight-level change consisting merely of an increase of the ambientlighting of the warehouse where the flame detector 10 is installed. Suchan increase in lighting will naturally occur within the prescribed area24, and more particularly at the point 28 within this area as well as atother points in this area. As a consequence, this increase in ambientlighting will effect both the photocells l2 and 14 in a similar mannerand will produce a generated voltage from both of these photocells whichwill be substantially of the same extent. Since the photocells l2, 14,as already noted, are connected in opposition to each other, thevoltages generated by these cells in response to an increase in ambientlighting will cancel each other out and thus there will be no currentflow in the conductor 22 that will result in operation of the fire alarm18. The foregoing, of course, will also be the result if there is adecrease, rather than an increase, in the ambient lighting.

Assuming, however, that fire starts at the flame-detection point 28,this occurrence of flame will naturally only significantly effect thephotocell 14. There thus will be generated .in the photocell 14 avoltage which is not similarly generated in the photocell 12, with theresult that there isan overbalance of generated voltage which, in turn,will produce current flow in the conductor 22. In any one of numerousways, this current flow can readily be made to trigger and thereby causeoperation of the fire alarm 18.

As a preferred but not necessarily essential technique in restricting orconfining the sensitivity of the flame detector 10 to the occurrence offlame at the flame-detection point 28, use is advantageously made ofred-transmission light filters 30, 32. Such a filter only passes redwavelength light and since redis the predominant color of flame, thephotocells 1.2, 14 are correspondingly rendered more sensitive to flame.

Reference is now made to the second embodiment of a flame detectoraccording to the present invention in which components similar to thesealready-described are designated by the same reference numeral.Embodiment l0 differs from the previously described embodiment of FIG. 1only in that the circuit components, particularly those related to thespecific forms of what were previously designated the fire alarm 18 andthe power supply 16, are more particularly illustrated in FIG. 2. Inthis embodiment, the resistors R2 and R3 are compensation resistors.Specifically, resistors R2 and R3 compensate for minimal ambient lightconditions for the photocells l2 and 14, whereas resistor R1 compensatesfor high ambient light-level changes which, in turn, will requiretriggering of the fire alarm in response to only a slight voltagedifference in the event of the occurrence of flame at the previouslynoted flame-detection point 28.

As illustrated, an overbalance of generated voltage results in currentflow to an operational amplifier A. Associated with the operationalamplifier A is a resistance R6 which permits adjustment of theoperational amplifier and thus adjustment in sensitivity of the completesystem. The output of the operational amplifier A is fed through a diodeD to a fire alarm triggering circuit. The function of the triggeringcircuit is to activate a buzzer or other alarm device connected inseries with it, in the illustrated embodiment, there being a lamp Lconnected across the buzzer BU which is optically coupled to a photocellin a conventional triac circuit T. Included in the triac circuit T arethe usual protection resistance and capacitors preventing damage fromexcessive inductive loads imposed on the triac.

Turning now to the power supply for the photocells l2, 14, asillustrated in FIG. 2, the same consists of a plus or minus volt supplyregulated by the illustrated diodes and transistors Z1, Z2. In theillustrated power supply, there is incorporated a safety featureconsisting of two I5-volt batteries decoupled through diodes D3 and D4which take over the supply of the system when AC power fails. On theother hand, when power is restored, the batteries are automaticallydecoupled out of the system.

In summary, the essential or inventive feature of the flame detector 10,illustrated in simplified form in FIG. 1 and in detail in FIG. 2,resides in its ability to react only to the occurrence of flame at theflame-detection point 28 and, more important, not to react in responseto mere ambient light-level changes. This is in sharp contrast topresently known optical flame detectors which when set to operate inresponse to the occurrence of flames in an environment characterized bya low ambient light level will invariably cause operation of the firealarm upon an increase change in this ambient light level. Moreover,where it is attempted to render the prior an flame detector inoperativewithin a certain range or change in the ambient light level, thissignificantly reduces the reaction time of the flame detector as well asits early sensitivity to the occurrence of flame at the flame-detectionpoint, and thus is not an entirely satisfactory solution.

A latitude of modification, change and substitution is intended in theforegoing disclosure and in some instances some features of theinvention will be employed without a corresponding use of otherfeatures.

What is claimed is:

1. A flame detector operatively arranged to supervise a remote referencearea by sounding a fire alarm in response to the presence of flameoccurring at a prescribed fire-detection point within said referencearea, said flame detector comprising a first photocell focused upon saidreference area without any light-blocking object interposed between itand said reference area so as to optically sense light-level changesoccurring in said reference area inclusive of said flame-detection pointand to generate an alarm-cancelling voltage corresponding thereto, acooperating arrangement of a lens and a second photocell similarlyfocused upon said reference area, said lens being optically effective tofurther restrict the focus of said second photocell only to saidflame-detection point within said reference area so as to restrict saidsecond photocell to the sensing of light-level changes occurring only atsaid flamedetection point and to generate an alarm-operating voltagecorresponding thereto, and separate circuits electrically arranged inopposing relation to each other connected between each of said first andsecond photocells and said fire alarm, whereby a light-level changeoccurring in said reference area of necessity also occurs at saidflame-detection point to thereby produce opposing alarm-operating andalarm-cancelling voltages of the same extent and which cancel each otherwhile a light-level change occurring only at said flamedetection pointonly produces an alarm-operating voltage which is effective to operatesaid alarm.

2. An optical flame detector as defined in claim 1 including ared-transmission light filter interposed between said prescribedflame-detection point and each of said photocells effective to limitsensitivity of said photocells to the predominant color of flame.

3. An optical flame detector as defined in claim 2 including anamplifier electrically connected between said first and said secondphotocells and said fire alarm effective to amplify any overbalance ofvoltage generated from said first photocell to an extent necessary tooperate said fire alarm.

1. A flame detector operatively arranged to supervise a remote referencearea by sounding a fire alarm in response to the presence of flameoccurring at a prescribed fire-detection point within said referencearea, said flame detector comprising a first photocell focused upon saidreference area without any light-blocking object interposed between itand said reference area so as to optically sense light-level changesoccurring in said reference area inclusive of said flame-detection pointand to generate an alarm-cancelling voltage corresponding thereto, acooperating arrangement of a lens and a second photocell similarlyfocused upon said reference area, said lens being optically effective tofurther restrict the focus of said second photocell only to saidflame-detection point within said reference area so as to restrict saidsecond photocell to the sensing of light-level changes occurring only atsaid flamedetection point and to generate an alarm-operating voltagecorresponding thereto, and separate circuits electrically arranged inopposing relation to each other connected between each of said first andsecond photocells and said fire alarm, whereby a light-level changeoccurring in said reference area of necessity also occurs at saidflame-detection point to thereby produce opposing alarm-operating andalarm-cancelling voltages of the same extent and which cancel each otherwhile a light-level change occurring only at said flame-detection pointonly produces an alarm-operating voltage which is effective to operatesaid fire alarm.
 2. An optical flame detector as defined in claim 1including a red-transmission light filter interposed between saidprescribed flame-detection point and each of said photocells effectiveto limit sensitivity of said photocells to the predominant color offlame.
 3. An optical flame detector as defined in claim 2 including anamplifier electrically connected between said first and said secondphotocells and said fire alarm effective to amplify any overbalance ofvoltage generated from said first photocell to an extent necessary tooperate said fire alarm.